public class DemoSpecies
1:
2:
3: import java.util.Scanner;
4:
5: /**
6: This version of the class Species is only a toy example designed
7: to demonstrate the difference between parameters of a class type
8: and parameters of a primitive type.
9: */
10: public class DemoSpecies
11: {
12: private String name;
13: private int population;
14: private double growthRate;
15:
16: /**
17: Tries to set intVariable equal to the population of the
18: calling object. But arguments of a primitive type cannot
19: be changed.
20: */
21: public void tryToChange(int intVariable)
22: {
23: intVariable = this.population;
24: }
25:
26: /**
27: Tries to make otherObject reference the calling object.
28: But arguments of a class type cannot be replaced.
29: */
30: public void tryToReplace(DemoSpecies otherObject)
31: {
32: otherObject = this;
33: }
34:
35: /**
36: Changes the data in otherObject to the data in this object,
37: which is unchanged.
38: */
39: public void change(DemoSpecies otherObject)
40: {
41: otherObject.name = this.name;
42: otherObject.population = this.population;
43: otherObject.growthRate = this.growthRate;
44: }
45:
46: public void readInput( )
47: {
48: Scanner keyboard = new Scanner(System.in);
49: System.out.println("What is the species’ name?");
50: name = keyboard.nextLine( );
51: System.out.println(
52: "What is the population of the species?");
53: keyboard = new Scanner(System.in);
54: population = keyboard.nextInt( );
55: while (population < 0)
56: {
57: System.out.println("Population cannot be negative.");
58: System.out.println("Reenter population:");
59: population = keyboard.nextInt( );
60: }
61: System.out.println(
62: "Enter growth rate (percent increase per year):");
63: growthRate = keyboard.nextDouble( );
64: }
65:
66: public void writeOutput( )
67: {
68: System.out.println("Name = " + name);
69: System.out.println("Population = " + population);
70: System.out.println("Growth rate = " + growthRate + "%");
71: }
72:
73: /**
74: Precondition: years is a nonnegative number.
75: Returns the projected population of the calling object
76: after the specified number of years.
77: */
78: public int predictPopulation(int years)
79: {
80: int result = 0;
81: double populationAmount = population;
82: int count = years;
83: while ((count > 0) && (populationAmount > 0))
84: {
85: populationAmount = (populationAmount +
86: (growthRate / 100) * populationAmount);
87: count--;
88: }
89: if (populationAmount > 0)
90: result = (int)populationAmount;
91:
92: return result;
93: }
94:
95: public void setSpecies(String newName, int newPopulation,
96: double newGrowthRate)
97: {
98: name = newName;
99: if (newPopulation >= 0)
100: population = newPopulation;
101: else
102: {
103: System.out.println("ERROR: using a negative population.");
104: System.exit(0);
105: }
106: growthRate = newGrowthRate;
107: }
108:
109: public String getName( )
110: {
111: return name;
112: }
113:
114: public int getPopulation( )
115: {
116: return population;
117: }
118:
119: public double getGrowthRate( )
120: {
121: return growthRate;
122: }
123:
124: public boolean equals(DemoSpecies otherObject)
125: {
126: return (name.equalsIgnoreCase(otherObject.name)) &&
127: (population == otherObject.population) &&
128: (growthRate == otherObject.growthRate);
129: }
130: }